Electromechanical actuators are used in a wide range of technology for actuating system parts, for example in engine, machine, vehicle or aviation technology.
An EMA motor comprises a stator assembly and a rotor. Power is supplied to the stator which results in generation of forces causing the rotor to rotate relative to the stator.
A stator assembly generally comprises a cylindrical back plate and a plurality of teeth extending radially inwards from the inner surface of the back plate. The teeth are separated by slots and electromagnetic coils are wound between the slots. The teeth surround a rotating central rotor having corresponding teeth. The resulting stator electromagnets are successfully energized by an external control circuit. As each electromagnet is powered, this creates an attractive force between the stator teeth and the rotor teeth to cause rotation of the rotor relative to the stator. A stator assembly generally consists of a set of magnetic steel laminations insulated from each other and glued, pressed or welded to form the stator core pack.
Laminations are slotted, and wound with typically copper wire to form one or more pairs of magnetic poles when energized by an external supply.
As the stator coils are energized they generate a magnetic field which will interact with the field produced by a set of magnets (in this case permanent magnets) placed on the motor rotor. The interaction between the two fields enables the motor to rotate.
Electromechanical actuators are finding increased use in applications where previously hydraulic actuators have been used, e.g. in aircraft, such as in the primary and secondary flight control actuators and nose wheel steering systems, and also in many other fields, such as elevators, ships etc.
Damping is often required in actuation systems or motor driven systems. For certain applications such as aileron, elevator or rudder for primary flight control or nose wheel steering damping function is required.
This function is necessary to prevent flutter of aerodynamic surface for an aileron, elevator and rudder in case of a power loss scenario. It also prevents hitting roughly the mechanical stops in the situation of wind gust.
For a nose wheel steering application damping will minimize nose wheel shimmy which is undesirable, and destructive.
Where hydraulic systems are used, the damping function is provided by a bypass restrictor. Where an EMA is used, however, there is no hydraulic fluid and so an alternative damping mechanism is required. Existing EMA systems have used a damper unit or component bolted on to the electric motor, e.g. to the motor shaft. This, whilst effective, increases the overall weight and size of the motor and involves increased manufacture time and costs.
The present invention aims to provide an improved electromechanical actuator motor damping arrangement.